The present invention relates to a method for treating spent silicon contact mass generated during the production of organohalosilanes by the direct reaction of organic halide with silicon powder in the presence of a copper catalyst.
Prior to the present invention, the disposition of unused spent silicon contact mass, generated during the production of organohalosilane by the direct reaction between silicon powder and an organic halide, such as aryl chloride or an alkyl halide for example methyl chloride, created a serious management problem for organohalosilane manufacturers. Spent silicon contact mass, for example, upon removal from the reactor can be highly reactive in air and often ignites.
One method for passivating or stabilizing spent silicon contact mass which can have an average particle size in the range of about 1 micron to about 200 microns and at least 2% by weight of copper in the elemental or chemically combined state, is shown by Hosokawa, U.S. Pat. No. 4,724,122. Hosokawa combines the spent silicon powder with water, granulates the resulting mixture, and thereafter mixes and/or coats the resulting granules with an inert inorganic powder. Another passivating technique for spent silicon contact mass is shown by Marko et al., U.S. Pat. No. 5,000,934, which employs a strong base at an elevated temperature to digest the hydrophobic siloxane rich coating on the spent silicon contact mass in order to dislodge the carbon coating which forms around the spent bed particles. An additional procedure for deactivating spent silicon contact mass is shown by Ritzer, et al., U.S. Pat. No. 4,892,694, which involves pelletizing the spent silicon contact mass and the impregnation of the pellets with an organic binder in aqueous carrier to stabilize the spent silicon contact mass to make it safe for transportation and disposal.
Additional processes are provided for the recovery of Rochow Synthesis mixtures derived from sludge vessels, as shown by Offenlegungschrift DE 313 1732AI and U.S. Pat. No. 4,758,351 to Felder et al. Mixtures of silicon rich solids and liquid containing polysilanes are subjected to a heat treatment or hydrolysis. For purposes of the invention, sludge vessel synthesis mixtures having a large proportion of liquid polysilanes are to be distinguished from the previously discussed pyrophoric spent silicon contact masses wherein liquid direct process high-boiling materials are not present as a constituent.
There is shown in copending application Ser. No. 07/867,657, filed Apr. 13, 1992, a method for passivating spent silicon contact mass by heating the spent silicon contact mass at a temperature in the range of about 900.degree. C. to about 1400.degree. C. under an inert atmosphere.
Although various procedures are available in the prior art for deactivating pyrophoric spent silicon contact mass generated during the direct method for making organohalosilanes, salvaging of the silicon and metallic values, such as copper, from the contact mass after the deactivation treatment is often not feasible. Additional procedures are therefore constantly being investigated to provide for safe handling of the spent silicon contact mass as well as the salvaging of the metallic values from the contact mass in a convenient manner.